To a solution of 4.59 g of phosphorous oxybromide (16 mmol) in 25 ml of anhydrous acetonitrile were added 1.11 g of 1,4-dihydroxy-7-phenylsulfanyl-isoquinoline-3-carboxylic acid butyl ester (3 mmol) and the mixture was refluxed gently with stirring for 1 h. Then 5.04 g of sodium bicarbonate (60 mmol) were added, followed by the dropwise addition of 8 ml of water. After stirring at ambient temperature for 90 min the mixture was concentrated in vacuo to about one third of its volume, 40 ml of water were added and the mixture was extracted with 30 ml of ethyl acetate. The mixture was filtered by suction. The organic phase was separated, dried over MgSO4, and filtered through a pad of silica gel. Evaporation in vacuo gave 0.885 g of the title compound; 1H NMR (CDCl3): δ=11.84 (s, 1H), 8.21 (d, 1H), 7.91 (d, 1H), 7.40 to 7.55 (m, 6H), 4.46 (t, 2H), 1.84 (m, 2H), 1.48 (m, 2H), 0.98 (t, 3H).
